Cervical plate locking mechanism and associated surgical method

ABSTRACT

The cervical plate locking mechanism of the present invention is elegant in its design and effective in its performance, and utilizes a plate with holes that each incorporate a locking lip structure and locking screws that each incorporate a head portion having petal structures that are outwardly biased prior to insertion via an internally-disposed c-ring or the like. Advantageously, the lead-in torque of each of the locking screws is less than the lead-out torque of each of the locking screws. Thus, reverse threading or backing out is prevented.

FIELD OF THE INVENTION

The present invention relates generally to a cervical plate locking mechanism and an associated surgical method. More specifically, the present invention relates to a cervical plate locking mechanism that includes one or more novel locking screws and a novel plate that works cooperatively therewith. The cervical plate locking mechanism, the one or more novel locking screws, and the novel plate are used for the fixation/stabilization of the cervical spine; alternatively, the fixation/stabilization of the lumbar spine; alternatively, the fixation/stabilization of the sacral spine; the placement of bone grafts, biocompatible inserts, or the like; alternatively, the fixation/stabilization of other anatomical structures; and, alternatively, the fixation/stabilization of other non-anatomical structures.

BACKGROUND OF THE INVENTION

The vertebrae of the human spine are generally arranged in a column, with an intervertebral disc disposed between each. These intervertebral discs transmit forces and perform a “cushioning” function. As a result of the stresses and strains continuously applied to the intervertebral discs, as well as disease, degeneration and/or deformity is relatively common. Typically, diseased, degenerated, and/or deformed intervertebral discs are treated by removal and the insertion of an implant, anatomical (i.e. a bone graft) or mechanical (i.e. a biocompatible insert), in the associated intervertebral space. The adjacent vertebrae are preferably immobilized using a plate, such as a cervical plate, during bone graft or biocompatible insert placement and subsequently until they fuse, for example.

Conventional cervical plates typically include a plurality of screw holes and one or more access holes, through which one or more bone grafts or other biocompatible inserts are placed. These cervical plates may span one or multiple levels, with a level defined by the presence of an intervertebral space, and are secured to the vertebrae of the spine using a plurality of bone screws. Absent some sort of locking mechanism, these bone screws tend to reverse thread, or back out, over time. This reverse threading or backing out is obviously problematic. Various locking mechanisms exist in the art for preventing reverse threading or backing out, and typically involve the use of polymeric bushings, securing caps, securing cover plates, novel thread designs, and the like that prevent the bone screws from disengaging the vertebrae and/or cervical plate subsequent to installation. Many of these locking mechanisms are ineffective, overly complicated, cumbersome to implement, and/or unnecessarily expensive. Thus, what is still needed in the art is a robust, simple, and inexpensive cervical plate locking mechanism.

BRIEF SUMMARY OF THE INVENTION

In various exemplary embodiments, the present invention provides such a robust, simple, and inexpensive cervical plate locking mechanism. The cervical plate locking mechanism of the present invention is elegant in its design and effective in its performance, and utilizes a plate with holes that each incorporate a locking lip structure, or receiving well, and locking screws that each incorporate a head portion having petal structures that are outwardly biased prior to insertion via an internally-disposed c-ring or the like. Advantageously, the lead-in torque of each of the locking screws is less than the lead-out torque of each of the locking screws. Thus, reverse threading or backing out is prevented.

In one exemplary embodiment, the present invention provides a cervical plate locking mechanism, including: a plate defining one or more holes configured to receive one or more locking screws, wherein the plate includes an outer surface, an interior portion, and an inner surface, each of the one or more holes having an inside diameter that is smaller adjacent to the outer surface than at the interior portion, thereby forming a lip structure associated with each of the one or more holes adjacent to the outer surface; and one or more locking screws, each including: a threaded portion configured to pass through one of the one or more holes of the plate and securely engage an anatomical structure; and a head portion attached to the threaded portion configured to securely engage the lip structure associated with one of the one or more holes of the plate. Preferably, the interior of the plate at each of the one or more holes is curved such that a lead-in torque of each of the one or more locking screws is less than a lead-out torque of each of the one or more locking screws. The head portion of each of the one or more locking screws includes a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures including an inner groove disposed adjacent to the central driver bore. Optionally, the plurality of petal structures disposed about the central driver bore are outwardly biased. Each of the one or more locking screws also includes a c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore. Each of the one or more holes defined by the plate is configured to receive one of the one or more locking screws one of perpendicularly and at an angle.

In another exemplary embodiment, the present invention provides a method for using a cervical plate locking mechanism, including: providing a plate defining one or more holes configured to receive one or more locking screws, wherein the plate includes an outer surface, an interior portion, and an inner surface, each of the one or more holes having an inside diameter that is smaller adjacent to the outer surface than at the interior portion, thereby forming a lip structure associated with each of the one or more holes adjacent to the outer surface; and providing one or more locking screws, each including: a threaded portion configured to pass through one of the one or more holes of the plate and securely engage an anatomical structure; and a head portion attached to the threaded portion configured to securely engage the lip structure associated with one of the one or more holes of the plate. Preferably, the interior of the plate at each of the one or more holes is curved such that a lead-in torque of each of the one or more locking screws is less than a lead-out torque of each of the one or more locking screws. The head portion of each of the one or more locking screws includes a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures including an inner groove disposed adjacent to the central driver bore. Optionally, the plurality of petal structures disposed about the central driver bore are outwardly biased. Each of the one or more locking screws also includes a c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore. Each of the one or more holes defined by the plate is configured to receive one of the one or more locking screws one of perpendicularly and at an angle.

In a further exemplary embodiment, the present invention provides a cervical plate locking mechanism, including: a plate defining one or more holes configured to receive one or more locking screws, wherein the plate includes an outer surface, an interior portion, and an inner surface, each of the one or more holes having an inside diameter that is smaller adjacent to the outer surface than at the interior portion, thereby forming a lip structure associated with each of the one or more holes adjacent to the outer surface; and one or more locking screws, each including: a threaded portion configured to pass through one of the one or more holes of the plate and securely engage an anatomical structure; a head portion attached to the threaded portion configured to securely engage the lip structure associated with one of the one or more holes of the plate, wherein the head portion of each of the one or more locking screws includes a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures including an inner groove disposed adjacent to the central driver bore, wherein the plurality of petal structures disposed about the central driver bore are outwardly biased; and a c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore. Preferably, the interior of the plate at each of the one or more holes is curved such that a lead-in torque of each of the one or more locking screws is less than a lead-out torque of each of the one or more locking screws. Each of the one or more holes defined by the plate is configured to receive one of the one or more locking screws one of perpendicularly and at an angle.

In a still further exemplary embodiment, the present invention provides a cervical plate locking mechanism, including: one or more locking screws, each including: a threaded portion configured to pass through one of one or more holes of a plate and securely engage an anatomical structure; a head portion attached to the threaded portion configured to securely engage a structure associated with one of the one or more holes of the plate, wherein the head portion of each of the one or more locking screws includes a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures including an inner groove disposed adjacent to the central driver bore, wherein the plurality of petal structures disposed about the central driver bore are outwardly biased; and a c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components and/or method steps, as appropriate, and in which:

FIG. 1 is an exploded perspective view of one exemplary embodiment of the cervical plate locking mechanism of the present invention (being installed using a keyed screwdriver or the like), the cervical plate locking mechanism including both novel plate and novel locking screw designs;

FIG. 2 is an exploded perspective view of one exemplary embodiment of the novel locking screw design of FIG. 1, the locking screw including a head portion that incorporates a plurality of petal structures that are outwardly biased by an internally-disposed c-ring or the like;

FIG. 3 is a perspective view of the novel locking screw design of FIGS. 1 and 2, the locking screw being in its “as inserted” state, with the c-ring being installed and the head portion being compressed;

FIG. 4 is a partial cross-sectional view of the cervical plate locking mechanism of FIG. 1, the novel locking screw of FIGS. 1-3 in the process of being inserted into the novel plate of FIG. 1;

FIG. 5 is a partial cross-sectional view of the cervical plate locking mechanism of FIGS. 1 and 4, the novel locking screw of FIGS. 1-4 being fully inserted into the novel plate of FIGS. 1 and 4; and

FIG. 6 is a partial cross-sectional view of the cervical plate locking mechanism of FIGS. 1, 4, and 5, the novel locking screws of FIGS. 1-5 being inserted into the novel plate of FIGS. 1, 4, and 5 at various exemplary angles.

DETAILED DESCRIPTION OF THE INVENTION

As described above, in various exemplary embodiments, the present invention provides a robust, simple, and inexpensive cervical plate locking mechanism. The cervical plate locking mechanism of the present invention is elegant in its design and effective in its performance, and utilizes a plate with holes that each incorporate a locking lip structure, or receiving well, and locking screws that each incorporate a head portion having petal structures that are outwardly biased prior to insertion via an internally-disposed c-ring or the like. Advantageously, the lead-in torque of each of the locking screws is less than the lead-out torque of each of the locking screws. Thus, reverse threading or backing out is prevented.

FIG. 1 is an exploded perspective view of one exemplary embodiment of the cervical plate locking mechanism 10 of the present invention (being installed using a keyed screwdriver 18 or the like), the cervical plate locking mechanism 10 including both novel plate and novel locking screw designs, as are described in greater detail herein below. Specifically, the cervical plate locking mechanism 10 includes a plate 12 that is configured to be securely fixed to adjacent vertebrae of the cervical spine or the like via one or more locking screws 14 and one or more c-rings 16. The keyed screwdriver 18 is used to drive the one or more locking screws 14 through the plate 12 and into the adjacent vertebrae. The plate 12 includes one or more screw-receiving holes 13 and, optionally, one or more access holes 15 for the placement of one or more bone grafts, biocompatible inserts, or the like. Preferably, the plate 12 is manufactured from a biocompatible material and is sized such that it achieves its intended purpose. Material, shape, and size selection is well known to those of ordinary skill in the art. Each of the one or more locking screws 14 includes a threaded portion 17 and a head portion 19. The threaded portion 17 of each of the one or more locking screws 14 is configured to pass through the one or more screw-receiving holes 13 of the plate 12 and securely fix the plate 12 to the adjacent vertebrae. Thread selection is well known to those of ordinary skill in the art. The head portion 19 of each of the one or more locking screws 14 is configured to securely engage each of the one or more locking screws 14 with the plate 12. As described in greater detail herein below, the head portion 19 of each of the one or more locking screws 14 is outwardly biased by the c-ring 16, or by another comparable mechanism, which is selectively compressed, inserted into the head portion 19 of a given locking screw 14, and then allowed to expand. The c-ring 16, or other comparable mechanism, and the head portion 19 of the given locking screw 14 are again compressed and subsequently allowed to expand as they are inserted into a given screw-receiving hole 13 of the plate 12. Specifically, the head portion 19 of the given locking screw 14 is allowed to expand in the receiving well of the given screw-receiving hole 13. This insertion is accomplished using a matching flat, triangle, square, star, hexagon, octagon, or other keyed screwdriver 18, as appropriate. Preferably, the shape of the outside of the head portion 19 of each of the locking screws 14 substantially corresponds to the shape of the inside of the associated receiving well, although this is not a requirement.

FIG. 2 is an exploded perspective view of one exemplary embodiment of the novel locking screw design of FIG. 1, the locking screw 14 including a head portion 19 that incorporates a plurality of petal structures 20 that are outwardly biased by the internally-disposed c-ring 16 or the like. As described above, the c-ring 16, or other comparable mechanism, is selectively compressed, inserted into the head portion 19 of a given locking screw 14, and then allowed to expand. The c-ring 16, or other comparable mechanism, and the head portion 19 of the given locking screw 14 are again compressed and subsequently allowed to expand as they are inserted into a given screw-receiving hole 13 (FIG. 1) of the plate 12 (FIG. 1). Specifically, the head portion 19 of the given locking screw 14 is allowed to expand in the receiving well of the given screw-receiving hole 13. This insertion is accomplished using a matching flat, triangle, square, star, hexagon, octagon, or other keyed screwdriver 18 (FIG. 1), as appropriate. Preferably, the shape of the outside of the head portion 19 of each of the locking screws 14 substantially corresponds to the shape of the inside of the associated receiving well, although this is not a requirement. Accordingly, the head portion 19 of each of the locking screws 14 includes a plurality of concentrically-arranged petal structures 20 that are disposed around a central driver bore 21 that has a shape corresponding to that of the keyed screwdriver 18. In one exemplary embodiment, the plurality of petal structures 20 are formed by cutting concentrically-arranged slots into the head portion 19 of the locking screw 14. Thus, the plurality of petal structures 20 are integrally formed with the head portion 19 of the locking screw 14. Alternatively, the plurality of petal structures 20 are formed separately and then joined to the head portion 19 of the locking screw 14. The material characteristics or configuration of the plurality of petal structures 20 may impart the plurality of petal structures 20 with an inherent outward bias, independent of the c-ring 16 or other comparable mechanism, although this is not required. Preferably, the plurality of petal structures 20 define an inner groove 22 that is configured to receive and retain the c-ring 16 or other comparable mechanism within the head portion 19 of the locking screw 14. FIG. 2 illustrates the head portion 19 of the locking screw 14 in an “unlocked” configuration, with the plurality of petal structures 20 being “open,” either due to the eventual insertion of the c-ring 16 or other comparable mechanism, or inherently. FIG. 3 illustrates the head portion 19 of the locking screw 14 in a “locked” configuration, with the plurality of petal structures 20 being “closed,” either inherently or due to the eventual insertion of the head portion 19 of the locking screw 14 into a receiving well.

FIG. 4 is a partial cross-sectional view of the cervical plate locking mechanism 10 of FIG. 1, the novel locking screw 14 of FIGS. 1-3 in the process of being inserted into the novel plate 12 of FIG. 1. It should be noted that the head portion 19 of the locking screw 14, and specifically the lower, outer portion of each of the plurality of petal structures 20, optionally incorporates a recessed or otherwise weakened area 24, or flexure, in order to facilitate the flexibility and/or outward biasing of the plurality of petal structures 20 by the c-ring 16 or other comparable mechanism, after it is inserted into the inner groove 22 that is manufactured into the middle, inner portion of each of the plurality of petal structures 20. Each of the one or more screw-receiving holes 13 of the plate 12 includes an annular lip structure 26 through which the head portions 19 of the locking screws 14 are inserted (with a compression - expansion action). This annular lip structure 26 serves to retain the head portion 19 of the given locking screw 14 once it is fully inserted and expanded, thereby preventing the reverse threading or backing out of the locking screw 14. Optionally, the inner annular surface 28 of each of the screw-receiving holes 13 of the plate 12 is curved in a generally concave manner, but shaped such that the lead-in torque of a given locking screw 14 is less than the lead-out torque or the locking screw 14, i.e. the inner annular surface angles adjacent to the outer surface 29 of the plate 12 (at the “top” and “bottom” of the lip structure 26) vary as experienced by an inserted locking screw 14 versus a removed locking screw 14, with the “top” angle being greater (more vertical or steep) and the “bottom” angle being smaller (more horizontal or shallow), for example.

FIG. 5 is a partial cross-sectional view of the cervical plate locking mechanism 10 of FIGS. 1 and 4, the novel locking screw 14 of FIGS. 1-4 being fully inserted into the novel plate 12 of FIGS. 1 and 4. Again, it should be noted that the head portion 19 of the locking screw 14, and specifically the lower, outer portion of each of the plurality of petal structures 20, optionally incorporates a recessed or otherwise weakened area 24, or flexure, in order to facilitate the flexibility and/or outward biasing of the plurality of petal structures 20 by the c-ring 16 or other comparable mechanism, after it is inserted into the inner groove 22 that is manufactured into the middle, inner portion of each of the plurality of petal structures 20. Each of the one or more screw-receiving holes 13 of the plate 12 includes an annular lip structure 26 through which the head portions 19 of the locking screws 14 are inserted (with a compression—expansion action). This annular lip structure 26 serves to retain the head portion 19 of the given locking screw 14 once it is fully inserted and expanded, as illustrated, thereby preventing the reverse threading or backing out of the locking screw 14. Optionally, the inner annular surface 28 of each of the screw-receiving holes 13 of the plate 12 is curved in a generally concave manner, but shaped such that the lead-in torque of a given locking screw 14 is less than the lead-out torque or the locking screw 14, i.e. the inner annular surface angles adjacent to the outer surface 29 of the plate 12 (at the “top” and “bottom” of the lip structure 26) vary as experienced by an inserted locking screw 14 versus a removed locking screw 14, with the “top” angle being greater (more vertical or steep) and the “bottom” angle being smaller (more horizontal or shallow), for example.

FIG. 6 is a partial cross-sectional view of the cervical plate locking mechanism 10 of FIGS. 1, 4, and 5, the novel locking screws 14 of FIGS. 1-5 being inserted into the novel plate 12 of FIGS. 1, 4, and 5 at various exemplary angles relative to both the plate 12 and the underlying vertebrae. In this embodiment, each of the receiving wells may be asymmetrical in shape such that the head portion 19 of each of the locking screws 14 snugly and securely engages the receiving well, although this is not necessarily illustrated. In other words, each of the receiving wells may be appropriately angled in the plate 12 in order to receive each of the angled locking screws 14.

Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims. 

What is claimed is:
 1. A cervical plate locking mechanism, comprising: a plate defining one or more holes configured to receive one or more locking screws, wherein the plate comprises an outer surface, an interior portion, and an inner surface, each of the one or more holes having an inside diameter that is smaller adjacent to the outer surface than at the interior portion, wherein the interior portion comprises a concave surface thereby forming a lip structure associated with each of the one or more holes adjacent to the outer surface, wherein a bottom portion of the lip structure is defined in part by the concave surface; and one or more locking screws, each comprising: a threaded portion configured to pass through one of the one or more holes of the plate and securely engage an anatomical structure; and a head portion comprising a top surface, bottom surface, and a side surface extending between the top surface and the bottom surface, wherein the head portion is attached to the threaded portion configured to securely engage the lip structure associated with one of the one or more holes of the plate, and wherein the plate is configured such that the top surface engages a portion of the concave surface defining the lip structure to securely engage the head portion within a hole of the one or more holes of the plate.
 2. The cervical plate locking mechanism of claim 1, wherein an interior of the plate at each of the one or more holes is curved such that a lead-in torque of each of the one or more locking screws is less than a lead-out torque of each of the one or more locking screws.
 3. The cervical plate locking mechanism of claim 1, wherein the head portion of each of the one or more locking screws comprises a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures comprising an inner groove disposed adjacent to the central driver bore, and each of the plurality of petal structures having a recessed flexure manufactured into its base for promoting the deflection thereof with respect to the head portion of the associated locking screw.
 4. The cervical plate locking mechanism of claim 3, wherein the plurality of petal structures disposed about the central driver bore are outwardly biased.
 5. The cervical plate locking mechanism of claim 3, wherein each of the one or more locking screws further comprises an outwardly biased c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore against the interior portion of each of the one or more holes of the plate.
 6. The cervical plate locking mechanism of claim 1, wherein each of the one or more holes defined by the plate is configured to receive one of the one or more locking screws one of perpendicularly and at an angle.
 7. A method for using a cervical plate locking mechanism, comprising: providing a plate defining one or more holes configured to receive one or more locking screws, wherein the plate comprises an outer surface, an interior portion, and an inner surface, each of the one or more holes having an inside diameter that is smaller adjacent to the outer surface than at the interior portion, wherein the interior portion comprises a concave surface thereby forming a lip structure associated with each of the one or more holes adjacent to the outer surface, wherein a bottom portion of the lip structure is defined in part by the concave surface; providing one or more locking screws, each comprising: a threaded portion configured to pass through one of the one or more holes of the plate and securely engage an anatomical structure; and a head portion comprising a top surface, bottom surface, and a side surface extending between the top surface and the bottom surface, wherein the head portion is attached to the threaded portion configured to securely engage the lip structure associated with one of the one or more holes of the plate; and inserting one or more locking screws into the one or more holes of the plate such that the head portion passes by the lip structure and such that the top surface of the head portion engages a portion of the concave surface defining the lip structure to securely engage the head portion within a hole of the one or more holes of the plate to prevent the one or more locking screws from backing out of the one or more holes.
 8. The method of claim 7, wherein an interior of the plate at each of the one or more holes is curved such that a lead-in torque of each of the one or more locking screws is less than a lead-out torque of each of the one or more locking screws.
 9. The method of claim 7, wherein the head portion of each of the one or more locking screws comprises a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures comprising an inner groove disposed adjacent to the central driver bore, and each of the plurality of petal structures having a recessed flexure manufactured into its base for promoting the deflection thereof with respect to the head portion of the associated locking screw.
 10. The method of claim 9, wherein the plurality of petal structures disposed about the central driver bore are outwardly biased.
 11. The method of claim 9, wherein each of the one or more locking screws further comprises an outwardly biased c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore against the interior portion of each of the one or more holes of the plate.
 12. The method of claim 7, wherein each of the one or more holes defined by the plate is configured to receive one of the one or more locking screws one of perpendicularly and at an angle.
 13. A cervical plate locking mechanism, comprising: a plate defining one or more holes configured to receive one or more locking screws, wherein the plate comprises an outer surface, an interior portion, and an inner surface, each of the one or more holes having an inside diameter that is smaller adjacent to the outer surface than at the interior portion, thereby forming a lip structure associated with each of the one or more holes adjacent to the outer surface, wherein the lip structure is partially formed by a bottom surface; and one or more locking screws, each comprising: a threaded portion configured to pass through one of the one or more holes of the plate and securely engage an anatomical structure; a head portion comprising a top surface, wherein the head portion is attached to the threaded portion configured to securely engage the lip structure associated with one of the one or more holes of the plate by engagement of the top surface of the head portion with the bottom surface of the lip structure, wherein the head portion of each of the one or more locking screws comprises a plurality of petal structures disposed about a central driver bore, each of the plurality of petal structures comprising an inner groove disposed adjacent to the central driver bore, and each of the plurality of petal structures having a recessed flexure manufactured into its base for promoting the deflection thereof with respect to the head portion of the associated locking screw, wherein the plurality of petal structures disposed about the central driver bore are outwardly biased; and an outwardly biased c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore against the interior portion of each of the one or more holes of the plate.
 14. The cervical plate locking mechanism of claim 13, wherein an interior of the plate at each of the one or more holes is curved such that a lead-in torque of each of the one or more locking screws is less than a lead-out torque of each of the one or more locking screws.
 15. The cervical plate locking mechanism of claim 13, wherein each of the one or more holes defined by the plate is configured to receive one of the one or more locking screws one of perpendicularly and at an angle.
 16. A cervical plate locking mechanism, comprising: one or more locking screws, each comprising: a threaded portion configured to pass through one of one or more holes of a plate and securely engage an anatomical structure; a head portion attached to the threaded portion configured to securely engage a structure associated with one of the one or more holes of the plate, wherein the head portion of each of the one or more locking screws comprises a plurality of petal structures disposed about a central driver bore, wherein the plurality of petal structures defines a shape corresponding with the shape of a keyed portion of a keyed screwdriver, each of the plurality of petal structures comprising an inner groove disposed adjacent to the central driver bore, and each of the plurality of petal structures having a recessed flexure manufactured into its base for promoting the deflection thereof with respect to the head portion of the associated locking screw, wherein the plurality of petal structures disposed about the central driver bore are outwardly biased; and an outwardly biased c-ring selectively disposed within the inner groove disposed adjacent to the central driver bore, the c-ring configured to outwardly bias the plurality of petal structures disposed about the central driver bore against the interior portion of each of the one or more holes of the plate. 